1. Field of the Invention
The present invention pertains to the field of hard surface cleaners. More particularly, the invention pertains to hard surface cleaners which thicken upon dilution forming a gel-like foam during cleaning operations.
2. Description of the Related Art
In recent years, it has become increasingly desirable to utilize hard surface cleaners which have high viscosities to increase surface contact time, particularly on non-horizontal surfaces. Such liquid products are highly viscous compositions which are used as such, without dilution, or at most modestly diluted. Examples of such products are disclosed in U.S. Pat. Nos. 3,622,1; 3,793,221; 3,843,548; and 4,005,027 and West German Patent DE 3,940,604.
Most recently, attention has been focused upon the development of relatively low viscosity concentrates which thicken, or increase their viscosity, upon dilution to working concentrations Such concentrates are cost effective due to their decreased packaging, transportation, and storage costs. Such concentrates are particularly useful for cleaning operations in the food industry. Several publications address thickening technology, for example H. Hoffmann, Progr. Colloid Polym. Sci. 84, pp 24-35 (1991); H. Hoffmann, Progr. Colloid Polym. Sci. 83 16-28 (1990); T. Imac and S. Ikada, Coll. and Pol. Sci. 13 134 (1985). Thickening technology is further described in European Patents EP 0 265 979, and EP 0 276 501; Great Britain Patent GB 2071688, and West German Patent DE 2359095.
In European patent application EP 0 314 232 compositions are described which thicken upon dilution, and which contain a primary surfactant which may be, inter alia, an amine oxide surfactant or a co-surfactant thereof which may be anionic. However, these compositions, in order to perform their intended function, contain relatively large amounts of amine oxide surfactants, i.e. from 8 to greater than 18 weight percent in the concentrate. The concentrates are then diluted to form working solutions containing from 5 to 15 weight percent of the concentrate. Such compositions are not economical in view of the large concentration of surfactant required of both the concentrate and the working solution. Furthermore, both the final use viscosity as well as the cleaning efficiency is less than desirable. In order to compensate, chlorine bleaches must be added, raising environmental concerns.